Continuing advances in magnetic storage technology provide for constantly increasing data storage densities. It is desirable to reduce the size of transducers used to read or write to magnetic media so that data densities can be increased. Magnetoresistive (MR) heads have been employed to reduce transducer size. Magnetoresistive heads comprise conductive thin films formed on a substrate using techniques similar to those used in manufacturing semiconductors.
A problem with all magnetoresistive heads is unstable magnetic domain states which lead to noise and error rate problems. When a magnetoresistive head is being used to write to magnetic media, or as the media moves relative to the head, a magnetoresistive element included in the head is subjected to external fields that tend to rotate magnetization away from its most stable orientation into orientations that can lead to multiple domain states.
A domain is a group of atoms organized into a bounded region. In each domain, magnetic moments of the atoms in that domain are aligned. Each domain is magnetically saturated and behaves like a magnet with its own magnetic moment and axis. It is undesirable to have multiple domain states in a magnetoresistive element of a magnetoresistive head.
One type of magnetoresistive head is a single stripe magnetoresistive head, which include a single magnetoresistive element. Single stripe magnetoresistive heads are typically shielded by soft magnetic and electrically conductive layers known as top and bottom shields.
One type of magnetoresistive head is a dual-stripe magnetoresistive head (DSMR). A dual-stripe magnetoresistive head includes two spaced apart magnetoresistive elements. Dual-stripe magnetoresistive heads are described in detail in U.S. Pat. Nos. 5,296,987 to Anthony et al.; 5,270,892 to Naberhuis; 5,079,831 to Reid; and 3,860,965 to Voegeli, which patents are incorporated herein by reference.
Another type of magnetoresistive head is a soft adjacent layer (SAL) head. Soft adjacent layer heads have been employed by International Business Machines (IBM) of Armonk, N.Y.
Another type of magnetoresistive head is a giant magnetoresistive (GMR) head. GMR heads are similar to SAL heads. GMR heads are described in detail in U.S. Pat. Nos. 5,446,613 to Rottmayer; and 5,442,508 to Smith, which patents are incorporated herein by reference.
One application for magnetoresistive heads is in analog audio applications. See, for example, a paper titled "Thin-Film Read Head for Analog Audio Application" by W. F. Druyvesteyn, L. Postma, G. H. J. Somers, and J. De Wilde, Philips Research Laboratories. This paper discloses that a main advantage of employing magnetoresistive heads is that photolithographic processing techniques can be used. The paper also describes that, when using a magnetoresistive head, signal is much higher at low frequencies than with an inductive head. Further, in automatic azimuth control audio recorders, where each audio track is read out with two separate heads, magnetoresistive heads provide the advantages of reduced crosstalk and reduced gap scatter. This paper also discusses a concept known as "magnetic feedback," in which a conductive layer is formed under a NiFe magnetoresistive element, and an electric current is passed through the conductor to generate a magnetic field opposite to the excitation field. This decreases distortion and Barkhausen noise.
Barkhausen noise is caused by an effect observed in ferromagnetic materials whereby magnetization proceeds as a series of finite jumps even though magnetizing flux is increased steadily. This happens because spin magnetic moments present in the material can only have certain orientations. The minute jumps correspond to the spin changing from one allowed orientation to another. Barkhausen noise is discussed in U.S. Pat. No. 5,296,987 to Anthony et al.
Construction details of magnetoresistive heads are known in the art, and will not be described in detail herein except as necessary to describe the invention. For example, in addition to the references described above, magnetoresistive heads are described in detail in U.S. Pat. Nos. 5,444,589 to Hu et al.; 5,422,571 to Gurney et al.; 5,442,507 to Koga et al.; U.S. Pat. No. 5,436,778 to Lin et al.; U.S. Pat. No 5,436,777 to Soeya et al.; 5,412,518 to Christner et al; and 5,142,425 to Gailbreath, Jr. et al., all of which are incorporated herein by reference. U.S. Pat. No. 5,309,304 discloses a variety of conductor arrangements that could be employed in various alternative embodiments of the instant invention.
Another application for magnetoresistive heads is in computer memory systems, such as disk drive memory systems of various sizes or formats, or magnetic tape memory systems of various sizes or formats. For example, it is known to employ magnetoresistive heads in computer hard disk drive systems. Conventional computer hard disk drives have a pivoting support arm that movably carries one or more actuator arms relative to one or more corresponding rotatable magnetic disks. Typically, both the top and bottom surfaces of each hard drive are configured to store tracks of information in the form of magnetic media provided on a surface of the hard disk. Therefore, each surface provides a unique data storage device. A support arm is pivoted into position by a rotary servo motor. Each actuator arm extends across the disk to position a magnetic head radially over concentric data tracks in the disk pursuant to position commands received from a drive controller.
The problem of unstable magnetic domain states also exists when magnetoresistive heads are employed in disk drive systems.